Mullen, Joseph P.; Mast, Amanda; Kounkel, Marina A.; Stassun, Keivan Guadalupe; Roman-Lopes, Alexandre; Tan, Jonathan C. (2025). A Galactic Interloper: A Study of the Camelopardis OB1 Association’s Clusters and Its Visitor from the Perseus Arm. Astrophysical Journal, 992(1), 17. https://doi.org/10.3847/1538-4357/adfb7a
Within the Camelopardalis OB1 (Cam OB1) region—a part of the Galaxy rich in young stars and gas—astronomers previously identified a single subgroup of stars. Recent Gaia data, however, reveal three distinct star clusters in roughly the same area of the sky (galactic longitude 137°–145°, latitude −2°–5°) and at a similar distance of about 1,000 parsecs (∼3,260 light-years).
This study identifies these three clusters, refines their membership lists, and estimates their ages, while examining their 3D structures, motions, and origins. Using Gaia measurements of positions and velocities, supplemented by radial velocities from the Sloan Digital Sky Survey, the clusters are found to be approximately 10, 15.8, and 20 million years old, containing about 140, 469, and 184 stars, respectively. Although the clusters currently overlap in space, tracing their motions backward shows that each formed in a distinct location, with no influence on the others’ formation.
Two clusters originated within the Cam OB1 region, while the oldest cluster formed near the edge of the Perseus Spiral Arm, in the direction of the Perseus OB1 or Cassiopeia OB6 associations. This work demonstrates how stellar groups from different parts of the Galaxy can pass through each other as they move through space.
Figure 1. IR (ALLWISE) color image in the direction of Cam OB1: red (W4), green (W2), and blue (W1). The four rectangles limit the areas of the associations Cassiopeia (Cas) OB6 and Perseus OB1 (Per OB1), located in the Perseus Arm, and the generic subgroups of Cam OB1 (including NGC 1502) as listed in literature. Overplotted are the three Cam OB1 cluster members as identified by this work.